Previously in shrinkDivRem64, it used fixed value 32 for AtLeast which
meant that <64bit divisions would be rejected from shrinking since logic
depended only on number of sign bits. I.e. 'idiv i48 %0, %1' would
return 24 for number of sign bits if %0,%1 both had 24 division bits,
and was rejected.

With the introduction of CmpPredicate in 51a895a (IR: introduce struct
with CmpInst::Predicate and samesign), PatternMatch is one of the first
key pieces of infrastructure that must be updated to match a CmpInst
respecting samesign information. Implement this change to Cmp-matchers.

This is a preparatory step in migrating the codebase over to
CmpPredicate. Since we no functional changes are desired at this stage,
we have chosen not to migrate CmpPredicate::operator==(CmpPredicate)
calls to use CmpPredicate::getMatching(), as that would have visible
impact on tests that are not yet written: instead, we call
CmpPredicate::operator==(Predicate), preserving the old behavior, while
also inserting a few FIXME comments for follow-ups.

This reverts commit 254d206ee2a337cb38ba347c896f7c6a14c7f218.

+Added a fix in ExpandDivRem24 to disqualify if DivNumBits exceed 24.

Original commit & msg:
ce6e955ac374f2b86cbbb73b2f32174dffd85f25.
Handle signed and unsigned path differently in getDivNumBits. Using
computeKnownBits, this rejects shrinking unsigned div/rem if operands
exceed signed max since we know NumSignBits will be always 0.

This reverts commit 509893b58ff444a6f080946bd368e9bde7668f13.

This broke the libc build again https://lab.llvm.org/buildbot/#/builders/73/builds/9787.

… (SignedMax,UnsignedMax] (#116733)"

This reverts commit 905e831f8c8341e53e7e3adc57fd20b8e08eb999.

Handle signed and unsigned path differently in getDivNumBits. Using
computeKnownBits, this rejects shrinking unsigned div/rem if operands
exceed signed max since we know NumSignBits will be always 0.

Rebased and re-attempt after first one was reverted due to unrelated
failure in LibC (should be fixed by now I'm told).

Use references instead of pointers for most state, initialize it all in
the constructor, and common up some of the initialization between the
legacy and new pass manager paths.

This reverts commit b8e1d4dbea8905e48d51a70bf75cb8fababa4a60.

Causes failures on the `libc` test suite https://lab.llvm.org/buildbot/#/builders/73/builds/8871

Do this by using ComputeKnownBits and checking for !isNonNegative and
isUnsigned. This rejects shrinking unsigned div/rem if operands exceed
smax_bitwidth since we know NumSignBits will be always 0.

Convert many instances of:
  Fn = Intrinsic::getOrInsertDeclaration(...);
  CreateCall(Fn, ...)
to the equivalent CreateIntrinsic call.